1. Field of the Invention
The present invention relates to an optical information reproducing apparatus which reproduces information stored in an information storage layer of a storage medium utilizing holography by illuminating the storage medium with reference light for reproduction; and an optical information storing/reproducing apparatus which stores information in an information storage layer of a storage medium by utilizing interference between information light carrying the information by spatial modulation and reference light for storage, and reproduces the stored information by illuminating the storage medium with reference light for reproduction.
2. Description of the Art
Conventionally, holographic storage which stores information in a storage medium by utilizing holography has been generally performed by overlapping information light carrying image information and reference light for storage in an information storage layer of the storage medium, and writing a resultant interference pattern in the storage medium. When the information which is stored in the information storage layer of the storage medium by utilizing the holography as above is reproduced, the storage medium is illuminated with reference light for reproduction, the reference light for reproduction is diffracted by the interference pattern in the information storage layer, reproduction light carrying the image information that the information light carried when the information was stored is generated, and therefore the image information is reproduced by detecting this reproduction light (refer to Japanese Unexamined Patent Application Publication No. H11-311938).
The reproduction light tracks back a light path of the reference light for reproduction. In the middle of the light path, the reproduction light is separated from the light path of the reference light for reproduction by a polarizing beam splitter, and proceeds toward a detector. Therefore, major part of the light path of the reproduction light is redundant with the light path of the reference light for reproduction.
When the information stored by using the conventional holographic storage is reproduced, much noise is found. One of the reasons for the noise is that not only the reproduction light having the image information, but also reflected light of the reference light for reproduction, which is reflected by a reflection layer of the storage medium is detected together with the reproduction light.
In order to reduce this noise, it has been considered to provide an aperture which removes the reflected light of the reference light for reproduction. However, as mentioned above, major part of the light path of the reference light for reproduction is redundant with the light path of the reproduction light. When the aperture is arranged at the redundant part, the reference light for reproduction itself which enters the storage medium is also shut out.
Therefore, the aperture has been conventionally arranged on the light path of the reproduction light only to remove the reflected light.
The conventional aperture to remove the reflected light is arranged on the light path of the reproduction light only. In this case, a distance between a reflection position of the reflected light and the aperture is long, and the reflected light is scattered in the middle of the distance. Therefore, the reflected light has not been removed sufficiently by the aperture.
Further, it is thinkable that not only the interference pattern is generated between the information light and the reference light for storage, but also an interference pattern is generated between the reference light for storage may arise, and this interference pattern between the reference light for storage may be stored as noise. As well as the interference between the reference light for storage which enters the storage medium, interference between the reflected light of the reference light for storage, which is reflected by the reflection layer of the storage medium is generated.